1. Field of the Invention
The present invention relates to a method and apparatus for primary synchronization in the Internet of things.
2. Description of Related Art
There is a wireless communication system that provides the Internet of things service over a wide area at low power and low cost based on an orthogonal frequency division multiplexing (OFDM) transmission scheme. The wireless communication system supports various modes such as a standalone operating mode, an in-band operating mode, and a guard band operating mode for versatility.
The standalone operating mode is a mode for operating a signal for providing the Internet of things service in a frequency band used in global system for mobile communication (GSM). The in-band operating mode is a mode for operating a signal for providing the Internet of things service to at least one of available resource blocks (RBs) in the frequency band used in the existing long term evolution (LTE) system. Further, the guard band operating mode is a mode for operating a signal for providing the Internet of things service to non-available RBs in a frequency band used in the existing LTE system.
The wireless communication system transmits the same primary synchronization signal every sixth subframe of each frame to acquire time synchronization and frequency synchronization irrespective of the operating modes described above. Describing in more detail, one frame consists of ten subframes and a narrowband primary synchronization signal (NPSS) is transmitted every sixth subframe of each frame. An NPSS frequency domain signal includes a total of 121 samples and values of the samples are fixed. The time synchronization and the frequency synchronization may be acquired by using a time domain conversion signal of the NPSS frequency domain signal.
If a cross-correlation method is generally used to acquire the time synchronization and the frequency synchronization, there is a problem in that battery consumption is increased. On the other hand, the auto-correlation method may reduce the battery consumption but has a problem in synchronization acquisition performance. Due to the problems, the existing method may not be suitable for the wireless communication system for providing the Internet of things service over a wide area for a long time.